Quick hints:

The fabric thread count is the number of threads in a linear inch of fabric. Even in metric countries,
fabric thread counts are per inch (that’s 2.54 cm). If your fabric is labelled "16-count", for example, just enter 16 as the
fabric thread count.

Stitching over 1 or 2: on aida or other coarse weaves you will normally stitch "over one" - each stitch crosses one thread. On linen and finer weaves you will normally stitch "over two".

The framing allowance is extra material that will not show after framing.
It’s there to let the framer do a good job of stretching the picture. This should be at least 3 inches.

Allow exposed borders if you also want some fabric to show between the picture and the frame, or want to
mat the picture. Usually it looks
best if the bottom border is a little larger than the top. You may like narrow side borders for a vertical
picture (longer than wide) and wide side borders for a horizontal picture. The fabric calculator shows you
how the work will look, so experiment!

The frame width does not affect the fabric calculation. It is just there so that you can tinker with
the aesthetics.